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See Saturn’s rings at their finest

The complex ring system is open wide during this year’s opposition, making it a prime time to explore the beautifully adorned gas giant.
RELATED TOPICS: AMATEUR ASTRONOMY | OBSERVING | SATURN
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Saturn’s rings are currently closing, a consequence of the planet’s 27° tilt and how our view of the world changes as it orbits the Sun. During every orbit, Saturn first presents one side of its rings to us, then, after a ring-plane crossing, the other. The 2022 opposition (similar to top right) will provide observers with fantastic views of the rings’ northern face before they start closing again over the next few years (bottom left).
NASA

Saturn, the ringed wonder, achieved opposition this year on Aug. 14 at 17h02m Universal Time (UT). With its rings currently 14° open, now is the perfect time to target the solar system's showpiece gas giant. It will be another five years before Saturn’s rings are again open enough (13°) to fully reveal all their components. 

Next year’s opposition (Aug. 27 at 8h20m UT) is also favorable, but the rings will open only 9° to our line of sight. That’s just narrow enough to limit the clarity of visual details, especially in the outermost ring, Ring A. This year’s opposition, then, marks the denouement of the northern face of Saturn’s rings. After this apparition, Saturn’s rings will gradually narrow until they turn edgewise in 2025; we will not see them open substantially again until 2027.

At opposition, Earth moves between Saturn and the Sun. With the ringed world rising as the Sun sets, this event marks when the planet is at its closest and brightest for the year. If you can’t make the actual date of opposition, don’t worry. For several nights leading up to and following that event, observers will still be able to view and image the finest details, not only in Saturn’s rings, but on the planet as well.

While Saturn virtually turns into “Super-Saturn” at opposition, the great gulf between it and Earth (nearly 824 million miles [1.33 billion kilometers], or 8.86 times the average Earth-Sun distance) causes it to shine modestly. At magnitude 0.3, Saturn will be about as bright as the star Procyon in Canis Minor. The world’s angular diameter is also demure at 18.8", which is less than half the diameter of Jupiter’s disk during its opposition.

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During its 29-year journey around the Sun, Saturn and its majestic ring system put on quite a show. These Hubble Space Telescope images, captured from 1996 to 2000 (bottom left to top right), reveal Saturn’s rings opening from just past edge-on to almost fully open.
NASA and The Hubble Heritage Team (STScI/AURA)

With a declination of –15.5° (in far eastern Capricornus, near the western border of Aquarius), this opposition favors the Southern Hemisphere, where observers will see the planet loom 60° above the horizon at its highest. From mid-northern latitudes, Saturn only climbs to half that altitude, making observations of it more susceptible to atmospheric turbulence.

Survey the rings

Saturn’s rings, as splendid as they appear in whole, require a careful eye to pick out fine details within. The illustration below shows its three main ring sections: Ring A (outermost), Ring B (middle), and Ring C (inner). Ring B is superior in brightness, followed by Ring A, and Ring C is the dimmest and most difficult of the trio to detect. Each of these sections contain subtle details, including ring divisions, variations in intensity and color, and many other curious aspects worthy of investigation.

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The summer Milky Way joins the planets Jupiter (brightest point of light) and Saturn (second brightest point of light) in the sky over the Badlands formations at the Trail of the Fossil Hunters site at Dinosaur Provincial Park, Alberta. The ground is illuminated thanks to a rising Last Quarter Moon off frame to the left.
Alan Dyer

Let’s look at each ring section individually, and I’ll describe some historical features that were regularly seen and imaged during last year’s opposition. Many of these features will likely be accessible again during this year’s apparition, with perhaps a few added bonuses. Note that as a general rule, viewing the features described in this article (unless otherwise noted) requires a quality telescope, eyepieces with magnifications of 250x or higher, and impeccable atmospheric seeing.

Wonders in the rings

At a glance, Ring A, the outermost of Saturn’s three main ring sections, appears like an ashen cap to brilliant Ring B. But a careful look with a magnifying power of roughly 100x or more will show the Cassini Division, a prominent dark gap (about 0.7" wide) separating rings A and B. And this year marks the penultimate chance to glimpse two other popular features before the ring-plane crossing occurs: the Encke Minima and Encke Gap.
The Encke Minima are not a true ring division, but instead a low-contrast feature (a dimming) caused by longitudinal variations in the ring’s density or transparency. They appear as broad fuzzy lanes in the middle of Saturn’s A ring. German astronomer Franz Encke made the first definitive records of them beginning April 25, 1837. On that night, using a 9.6-inch refractor, he noted that the “outer ring is divided by a line parallel to the edges into two very close equal parts from both sides.” Today, they are the most viewed and imaged feature in Ring A through 4-inch and larger telescopes.

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Saturn’s three major rings (A, B, and C), as well as two of the most sought-after ring divisions (the Encke Gap and the Cassini Division), are popular targets for amateur observers
NASA

The Encke Gap, on the other hand, is one of Ring A’s most elusive visual challenges. This hyperfine thread of darkness (a true gap) in the extreme outer portion of Ring A lies less than one-fifth of the ring from its outer edge. Saturn’s walnut-shaped moon Pan is responsible for keeping the 200-mile-wide (320 km) gap open. In January 1888, on a night of exceptional seeing, American astronomer James Keeler discovered the gap through the Lick Observatory 36-inch refractor at high power. 

Other observers had likely spied the Encke Minima and Encke Gap on earlier dates, but Encke and Keeler’s observations were the most definitive. Today, the Encke Gap is commonly seen and imaged through 10-inch and larger telescopes, though it has been viewed through smaller quality instruments at high power, as shown in the sketch on page 50 by David Graham of England.

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Franz Encke’s April 25, 1837, drawing shows brightness minima in the middle of Ring A on each ansa, the protruding parts of the planet’s rings.
Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin (1838)

Ring B, the brightest, densest, and most pronounced of Saturn’s rings, also displays the most texture, generally allowing observers to perceive plenty of detail. First impressions reveal that the ring gradually dims from a sandy white color in its outer portion, fading to a dusty beige color in its darker inner portion. Furthermore, as American astronomer Charles Wesley Tuttle described Oct. 20, 1851, the view through Harvard Observatory’s 15-inch Great Refractor at high power showed that Ring B was “minutely subdivided into a great number of narrow rings … not unlike a series of waves.”

This year’s opposition may also have a major surprise in store for us: Saturn’s spokes, which are mysterious streaks that cut across the rings. Astronomers think these spokes are made of micrometer-sized dust electrostatically held in place above the rings. They may be a seasonal phenomenon, appearing only during the low-angle lighting that occurs near equinox, namely when the rings are less than or equal to about 17° open. But no one knows for sure. Spokes have appeared and disappeared before, so the only way to catch them is to keep watch. As of early May, no spokes have been seen or imaged. But they could appear in time for opposition. It’s hard to say, as so little is known about these strange radial features. Note that if they do appear, they should be most prominent along the morning ansa (protruding “handle”) of Ring B.

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This drawing by David Graham of Richmond, North Yorkshire, England, shows details he spied while observing Saturn at 286x through a 6-inch refractor owned by Ohio amateur Tom Dobbins. Note the Encke Minima and Encke Gap in Ring A.
David Graham

A faint inner ring, or Ring C, has a milky transparency against the blackness of space. However, it appears as a dusky veil when seen against the globe of the planet, which is why it was known originally as the Crepe Ring. Astronomer George Phillips Bond of Harvard first suspected its “feebly illuminated” form Oct. 10, 1850. But he saw it “with full certainty” Nov. 11, not only as “a dark band in front of the planet,” but as the “filling up of light inside of the inner edge of the inner ring [B].”

Today, amateurs using quality telescopes as small as 3 inches have spied the feature in its entirety. It remains the least surveyed of Saturn’s main rings, though it could potentially be one of the most fascinating for study. Historical observations of Ring C have shown it to vary in color and intensity over time, as well as to display asymmetries, brightness anomalies, and spurious dark features. While some, or all, of these curiosities may be the result of optical effects or illusions, they are nonetheless worthy of further scrutiny.

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The record-groove effect seen in Saturn’s rings is most prominent in the brighter Ring B when seen through a telescope, as shown in the drawing by Charles Wesley Tuttle at left. The color differences in the rings are brought into stunning focus in the Cassini image at right. L
Left: Charles Wesley Tuttle/Harvard; Right: NASA/JPL/Space Science Institute

Seeliger effect and Ring A

In the days leading up to and around opposition, the rings of Saturn surge in brightness. It is one of the most visually alluring planetary phenomena, and it can be appreciated through the smallest of telescopes, perhaps even with the unaided eye. Generally, Saturn’s rings appear about as bright as the planet’s globe. In the days leading up to opposition, however, the rings suddenly outshine Saturn before dimming back to their normal appearance. German astronomer Hugo von Seeliger first noticed this change in 1887 and the phenomenon was named in his honor.

Two factors come into play to create the Seeliger effect. First, when we see Saturn directly illuminated by the Sun (as it is during opposition), the planet’s shadow “hides” behind the disk, placing more ring surface into view. As a result, the rings appear brighter. The same direct lighting angle also causes the shadows of individual particles in the rings to temporarily vanish, enhancing the effect.

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NASA’s Cassini spacecraft captured the mysterious spokes in Saturn’s Ring B on Oct. 19, 2008.
NASA/JPL/Space Science Institute

Second, Cassini spacecraft observations of the opposition effect in Saturn’s rings reveal that “coherent backscattering” also significantly contributes to the phenomenon. This occurs when sunlight interacts with the particles in the planet’s rings. Individual reflections off the many irregular bits of rock and dust combine to produce more coherent, intense light. This light scatters back to our eyes and makes the rings seem brighter. 

Saturn’s Ring A also displays alternating bright and dark quadrants, known as an asymmetrical azimuthal brightness variations. These features change in intensity depending on the ring elevation angle (between 26° and about 10°), reaching a peak amplitude near 10°. So, the effect may be particularly pronounced during this apparition; expect brightness differences of about 20 to 30 percent between the light and dark quadrants. It’s important to note that around opposition, the azimuthal effect appears to diminish. So, start your observations well before or after opposition.

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One of the author’s pre-spacecraft sketches of the observed spokes in Saturn’s Ring B is shown above. The spokes appeared on the morning ansa and were viewed through a 9-inch refractor at Harvard College Observatory Nov. 24, 1976.

Stephen James O’Meara

Study Saturn’s face

Compared to Jupiter, Saturn’s face is a more delicate object of study. While it too displays dark belts and bright zones, many are of low contrast. This is because we see them through a high-altitude haze in Saturn’s upper atmosphere, which hides the finer details beneath. But Saturn is known to surprise. Small scopes generally show the world's Equatorial Zone (by far the brightest), bordered by dark Equatorial Belts. The planet’s Tropical and Temperate regions are more difficult to define, and they generally appear as a wide, bright yellow wash. Meanwhile, the planet’s North Polar Region usually takes on a dusky appearance that gradually darkens toward the pole. However, early observations this year show the planet’s dark cap appearing like an island in a brighter polar region.

This somewhat placid view changes once one images the ringed planet under excellent seeing conditions or uses a larger high-quality telescope with substantial magnification. Then, much more structure pops into view, including intricate banding, different-colored zones and belts, and white-spot activity.

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Saturn’s tiny moon Pan (marked by arrow) steadily orbiting around the gas giant allows it to carve out a small path, called the Encke Gap, in the fringes of Ring A.
NASA/JPL-Caltech/Space science institute

Last apparition, Saturn’s face was well banded, with the North Polar Region taking on the appearance of a hexagon. Amateur astronomers were able to capture the North Polar Hexagon (within which resided a very small dark cap) on several instances. By this year’s opposition, however, the hexagon will likely recede from view. Overall, the yellow Equatorial Zone appeared brighter and more intensely colored to the north, while the dusky Equatorial Band was split on occasion. In some observations, the bright North North Temperate Zone (just south of the North Polar Region) persisted into November before solar conjunction.

This year, observers should also be on the alert for pronounced white-spot activity. White spots, which can vary dramatically in size and intensity, are the result of powerful atmospheric storms hurling water and other molecules high into Saturn’s atmosphere, where they freeze out to form white clouds. Two bright white spots detected in the North North Temperate Zone may have caused the zone to temporarily increase in brightness last apparition, and such activity appears to be ongoing early this time too. Several intriguing smaller white spots were also detected at varying latitudes last year, including one in the North Equatorial Belt, as well as a prolonged white spot and plume activity in the Equatorial Zone. Meanwhile, this year, as of early May, some low-contrast white spot activity has been imaged in the planet’s North Tropical Belt.

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The nomenclature for Saturn’s dark belts and bright zones is shown here, with the planet oriented north down.
NASA, ESA, Amy Simon (NASA-GSFC), Michael H. Wong (UC Berkeley); Processing: Alyssa Pagan (STScI)

So keep an eye out, because more intense white-spot activity potentially could be linked to spoke propagation. As planetary scientist Geraint Jones of University College London and his colleagues have proposed, energetic beams of electrons produced above powerful thunderstorms (related to white-spot activity) could be transported to the rings by Saturn’s magnetic field. There, the electrons charge the dust, lifting it out of the ring plane to create the spokes.

Whether you decide to study the details of Saturn’s face or not, don’t miss out on this year’s opposition display. After all, ask any observer and they’ll tell you: Views of the ringed world through instruments of all sizes never disappoint. It is the most beautiful planet in our solar system, no matter how much or little detail you seek.

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